Dear Joe

I’m kind of new at this powder coating technology thing and heard an unusual description for powders. One of my operators talked about “winter” powder versus “summer” powder. She said that they behave differently so it’s important to adjust your application settings to compensate for these differences. Is this true, or is it just another urban legend in the wonderful world of powder coatings?

Left Unsure of Manageable Powder Spraying

Dear LUMPS

Your operator has the story partially correct. Powders do behave differently depending on environmental conditions. The difference in application performance depends more on the environment in your application area than on the environmental conditions when the powder was manufactured. Certainly an arid day in the middle of January will influence your powder’s electrostatics, just as a sweltering, humid day in August will. Cold, dry air allows electrons to hang around longer than warm, moist air. On a cold, dry day, you may experience excess charge accumulation leading to back ionization, which occurs when a negative charge doesn’t dissipate quickly enough when a powder is electrostatically deposited. This phenomenon causes microbursts of powder on the substrate, kind of like mini volcanoes. The resultant coating surface resembles star patterns. Electrostatic powder seems to enjoy a certain amount of humidity. High relative humidity has a calming effect on the application properties. The only real enemy is excessive heat. Ambient temperatures over 100˚F can spell trouble with caking and sintering of powder coatings.

The other thing to avoid when handling powder is storing it in a very cool environment and then transferring it quickly to a hot and humid environment. Cool powder exposed to humid air will essentially act as a desiccant and adsorb the moisture from the air.

So there really isn’t a phenomenon of “winter” and “summer” powders. It’s the application environment that influences the performance, not the date that it was made.

Dear Joe

We've been asked to provide a coating for food bins that will be used to store bulk chocolates in a retail environment. Our customer would like these coated in white, orange and a baby blue. I was wondering if powder coatings can be used as a finish on containers that are intended for the storage of confectionary goods. Are there some do’s and dont’s I should be aware of?

Candy, Hershey, PA

Dear Candy

I’m glad you asked this question before you coated thousands of containers and then found out that the coating is not acceptable for contact with foodstuffs. Indeed, there is powder coating technology that can be used for finishes coming in contact with food or beverages. The good folks at the Food and Drug Administration (FDA) in Washington, DC, have developed a Code of Federal Regulations that specifically details what components can be used in a coating formula that is used in the food industry. It’s known as Title 21 CFR 175.300 — commonly referred to as the “white list” — and basically outlines what can be used in the resin and binder of the coating. Likewise, the pigments we can use are listed in CFR 178.3297. Powder coating technologists consult these documents when formulating for food contact applications.

As long as your coating supplier can vouch that the coating is based only on ingredients on the white list, then you’re in the clear. Typically this means you will be using either an epoxy or hybrid (epoxy polyester) powder coating. Your choice of color may be limited because not all pigments are listed in CFR 178.3297. Still, the possible color palette is quite broad.

Your next step is to dazzle your powder supplier with your newfound knowledge and get the right powder for your application.

Ask Joe Powder is a regular feature of Finishing Today magazine. Please send your questions to askjoepowder@yahoo.com